Large private data line networks which extend over a vast geographic area have become commonplace in environments requiring communication between a host computer located, for example, at the headquarters in one city and a multitude of data circuits concentrated in branch locations in other cities or remote areas. A typical example would be a large bank having branch offices and ATM machines at various remote locations. Other applications would include stock market quotation networks, airline reservation systems, tickets sales systems and large military installations.
Rather than running an individual line to each of the terminal locations, a high speed trunk line, comprising one or more individual lines, is used to serve data between the host computer and the various locations. A packet assembler and disassembler (PAD) is provided at a concentration of data circuits in a remote location. The PAD reroutes data packages from the high speed trunk line to the various local data circuits in accordance with addresses included in the data packets. Various standard interfaces are available including, for example, RS232, V.35 and T1.
Such large data networks require testing in the event of system troubles. Users often provide their own network operations centers and maintenance personnel to perform testing, monitoring and analysis. Circuit continuity checks can be done remotely and remote bit error rate testing provides the ability to loop back an individual circuit to see the error rate at which data that is sent out is received back correctly. While these test procedures determine whether data can be accurately transmitted, they do not enable monitoring and analyzing data actually transmitted during use. The transmission of the data may be performed flawlessly but if improper data is applied to the communication line such defect is not detected.
There is an extensive variety of problems which are not capable of diagnosis in such a testing environment. For example, a polling operation may not be functioning properly because the polled station address is incorrectly stored in the host computer memory or because there is a change or defect in the host software. As another example, communication may not be established because improper input data has been applied in a log in procedure. Another common problem that would not be discerned is the generation of erroneous data from a "streaming terminal." Such generation occurs when a data input key malfunctions or is continuously depressed.
Conventional systems do not have the ability remotely to analyze data link protocols and to perform network analysis, such as defined by the International Standards Organization as OSI model levels 2 and 3. That is, problems such as those just discussed are not diagnosed remotely. If protocol analysis or other diagnostics are to be performed, a technician must be dispatched with a portable protocol analyzer to several points along the circuit.
Use of the portable analyzer involves identification and selection of the line to be accessed, disconnection of the line, followed by reconnection with the analyzer inserted in circuit to perform analysis functions, and again disconnection to remove the analyzer from the circuit. The intrusive nature of this use, as well as the demands on the technician's time, are significant disadvantages of conventional practice. The results of the on site monitoring and collection of data often require more detailed analysis at the maintenance facility. Conveyance of such information to the facility in a timely manner may be costly and inconvenient.
These drawbacks are multiplied when a circuit exhibits a recurring problem that requires extended attention. For example, in a case of network administration, a circuit may be seen to malfunction frequently at the same time of day. A technician would have to personally attend the local site each day at the same time until the problem is diagnosed or, alternatively, remain at the site during the entire time. As an operating technician is required to be at the testing site, cost considerations restrict use to short, noncontinuous periods. Testing is normally done either on a routine basis or after indentification of the existence of a problem whose exact nature is not yet known. Conventional protocol analysis is therefore limited in that it can not practically be used to monitor the data stream of a selected circuit continuously over an extended period of time. Without such use, there is no pragmatic way to detect the occurrence of a predefined condition and to initiate a control function upon recognition of such occurrence.